(1) Field of Invention
Anti-jackknife device for tractor-trailer combinations.
(2) Prior Art
Heretofore anti-jackknife devices have been provided for tractor-trailer combinations. In general, in these prior structures, the tractor fifth wheel and its mounting must withstand severe turning moments imposed in resisting any tendency of the tractor and trailer to jackknife.
The conventional fifth wheel is one having a bearing plate with a central socket, with a cut-out in the plate leading into the socket and having guide edges divergent outwardly of the plate and which operate to guide the connecting pin on the trailer radially into the socket. Such fifth wheels have jaws which can be swung, selectively, out of locking position at the rear of the socket to permit the pin to enter radially into the socket, and into locking position behind the pin to retain it in the socket.
Prior anti-jackknife devices customarily are arranged with an element on the trailer which can be shifted selectively to a position to interpose a turn limiting lug on the trailer between the guiding edges on the fifth wheel, so that, upon relative turning of the tractor and trailer about the connecting pin beyond a predetermined degree, the lug engages one or the other of the guide edges of the fifth wheel and thereby limits the relative rotation or degree of turn of the tractor and trailer about the connecting pin.
Thus all of the stresses of the turning moments imposed in preventing jackknifing are resisted by reactive turning moments of the fifth wheel structure and its mounting. These stresses opposing turning moments by the fifth wheel about the connecting pin axis are at a relatively short radius from the turning axis, this radius being limited in length, at maximum, to the maximum radius of the fifth wheel bearing plate itself.